Relation between air and media temperature of containerized nursery crops

Media temperature (MT) of containerized plants has a distinct effect on crop growth and development, water and nutrient uptake and ultimately influences marketable quality. Containerized plants suffer due to a low root zone temperature during the winter and a high root zone temperature during the summer. Thus, in order to protect the crop from extreme root-zone temperatures, it is necessery to understand the overall behavior of media temperature. The objective of this study was to determine the relationship between the media temperature (MT) and the air temperature (AT) in containerized nursery crops under short irrigation intervals. The study was conducted during May, June, July and August of 2006 at Monrovia Growers, located in Cairo, GA. The experiment consisted of one plastic container size, i.e. 18.9-L, with five replicates. Media temperature was measured at 15-minute intervals, while air temperature and solar radiation were obtained from an automated weather station located 20 m from the experimental site. Irrigation was applied six times daily using a micro irrigation system consisting of micro sprayers (Spitters). The MT gradient and AT gradient were determined every two hours, from 6:00 am to 8:00 pm, for a total of 7 two-hour periods during 10 days in May, June, July, and August. For all 10-day periods during May, June, July, and August, a positive and significant (P < 0.05) correlation between air temperature gradient (ΔAT) and media temperature gradient (ΔMT) was found during the morning hours, whereas a negative and significant (P < 0.05) correlation was found for the same period of time in the afternoon. The correlation between ΔA T and ΔMT was affected by time lag between AT and MT. The relationship between ΔAT and ΔMT varied for different time periods during the day and for all 10-day periods that were analyzed. The maximum MT during the summer, i.e. 36.9°C, was lower than 40°C, which is considered critical for containerized crops. Short-interval irrigations successfully moderated the increase of the MT due to high ambient temperature events. Our results demonstrated that media temperature and air temperature have a significant relationship. However, this relationship seems to be a function of the time of the day. Further work will consider other variables in the analysis, such as media moisture and the temperature of the irrigation water.